Dimerization of cinnamic acid by ultraviolet radiation has been known for years. Therefore, it is conceivable that a useful photo-sensitive resin will be obtained by incorporating a cinnamoyl group into a polymer. Conventionally known as a polymer having a cinnamoyl group is polyvinyl cinnamate (polyvinyl having a cinnamoyl group) (Jpn. J. Appl. Phys., 31(1992), 2155, and J. Photopolymer Sci. and Tech. 8(1995), 257). The polyvinyl cinnamate is a useful photo-sensitive resin which becomes insoluble in a solvent when the cinnamoyl group is dimerized by light radiation (J. Appl. Polymer Sci., 2, 302(1959)), and used as a negative photo-sensitive resin.
However, the aforesaid polyvinyl cinnamate is poor in heat resistance and, hence, cannot be used in applications which require heat resistance.
Meanwhile, a reaction process is facilitated by first introducing a cinnamoyl group into a starting material of a polymer, i.e., a reactive monomer, and then polymerizing the monomer. However, no such reactive monomer is yet in existence.
Among a variety of organic polymers, polyimides and polyamides are particularly excellent resins which find wide applications in various fields ranging from the aerospace field to the electronic comunications field because of their superior heat resistance, and have been expected to be applicable to photo-sensitive resins.
In general, starting materials for an aromatic polyimide are an aromatic amine and an acid dianhydride, and starting materials for an aromatic polyamide are an aromatic amine and an aromatic dicarboxylic acid or an aromatic dicarboxylic acid chloride. An aromatic acid dianhydride having a cinnamoyl group has not been known yet.
The aromatic amine is generally obtained by reducing an aromatic nitro compound. For production of a polyimide or polyamide having a cinnamoyl group, an aromatic amine having the cinnamoyl group is first obtained by reduction of a nitro compound having the cinnamoyl group, and then polymerization is carried out to afford the polyimide or polyamide. However, processes for the reduction of the aromatic nitro compound into the aromatic amine currently suffer from the following drawbacks. Further, few amines which have the cinnamoyl group and are usable as monomers for photo-sensitive resin materials have been known, and neither polyimide nor polyamide exists which has the cinnamoyl group and is usable as a photo-sensitive resin.
Common processes for reducing an aromatic nitro compound into an aromatic amine include: (1) reduction with a metal or a metal salt; (2) reduction with hydrazine; (3) hydrogenation with a Pd-activated charcoal catalyst; and the like.
Examples of the process (1) include reduction with tin chloride in a hydrochloric acid solution (tin-hydrochloric acid system), reduction with iron sulfate followed by neutralization with ammonia (iron sulfate-ammonia system), and reduction with metal iron in a solution (Bechamp reduction).
In these processes, however, precipitation of metal salts results from neutralization upon completion of the reaction, so that a very troublesome operation is required in isolation of the aromatic amine. In addition, these processes suffer from a problem such that breakage of ester linkage may occur due to the reaction under acidic conditions or a Michael addition may occur due to the reaction under alkaline conditions.
Examples of the process (2) include hydrogenation with a Pd-activated charcoal catalyst, and hydrogenation with a Raney nickel catalyst.
Among these processes, the hydrogenation with the Pd-activated charcoal catalyst is not preferred because a side reaction such as a Michael addition or decomposition of a nitro compound may occur. One example of the hydrogenation with the Raney nickel catalyst is described in Heiv. Chim. Actra., 24, 209E (1941), in which aminocinnamic acid is synthesized from nitrocinnamic acid with the use of hydrazine in the presence of the Raney nickel catalyst. However, if this system is applied to reduction of a nitrocinnamic acid derivative instead of nitrocinnamic acid, a side reaction such as a Michael addition may proceed.
In the process (3), reduction is generally allowed to proceed with the use of a Pd-activated charcoal catalyst in an organic solvent under a hydrogen atmosphere. With the use of an ordinary Pd-activated charcoal, even a double bond of a cinnamoyl group may be reduced.
As described above, it is very difficult to optimize the conditions for the reduction of the nitro compound, so that few amines having the cinnamoyl group have been isolated.
In order to solve the aforesaid problems, the present invention is directed to provide a method for preparing a novel amine having a cinnamoyl group or a derived cinnamoyl group by optimizing conditions for reduction of a nitro compound, such a novel amine having been considered impossible to prepare.
It is an object of the present invention to provide a novel diamine or a novel acid dianhydride to provide a novel polyimide composition having a cinnamoyl group or a derived cinnamoyl group.
It is another object of the invention to provide a novel polyimide composition prepared from a novel diamine or a novel acid dianhydride having a cinnamoyl group or a derived cinnamoyl group.
It is further another object of the invention to provide a method for producing a novel diamine having a cinnamoyl group or a derived cinnamoyl group.